PROJECT SUMMARY/ABSTRACT The emergence of drug-resistant strains of human influenza A (IAV) and B viruses, as well as avian H5N1 virus with pandemic potential, to the only approved antiviral agents underscores the importance of developing novel antiviral strategies. We have engineered electrostatic complexes between cationic nanoparticles (i.e., chitosan) and anionic RNA that target airway epithelial cells in vivo during an IAV infection. These nanoplexes induce antiviral bioactivity directed against IAV in vivo with little or no untoward cellular or pulmonary responses. The nanoplex constructs stimulate early type I interferon (IFN) cellular responses through 5?- triphosphate (PPP)-RNA binding of the intracellular sensor, RIG-I. Additionally, the 5?PPP-NS1shRNA nanoplex formulation suppresses the translation of the IAV virulence factor, NS1, which inhibits RIG-I and host cell RNA maturation. The lung is well suited for an antiviral nanoplex strategy since it provides a portal for inhalation administration of bioactive nanoplexes. We have demonstrated that this strategy inhibits in vivo IAV replication therapeutically and avoids the ?IFN paradox?, specifically, decreasing IAV lung injury, and IAV impairment of bacterial clearance from the lung. The focus of the current proposal is to optimize the therapeutic action of the 5?PPP-NS1shRNA nanoplex formulation in vitro and then in vivo. Additionally, we propose to carry out experiments recommended by the FDA article entitled ?Antiviral Product Development: Conducting and Submitting Virological Studies to the Agency.? This includes in vitro and in vivo experiments to assess therapeutic efficacy (antiviral activity), pharmacokinetics, drug-drug interactions, and development of viral resistance. Additionally, because the 5?PPP-NS1shRNA nanoplex modulates the immune response, the FDA recommends examining possible unintended adverse effects resulting from actions on the immune system. Thus, we will also identify the specific immune system components that are altered, as well as assess the immune-mediated complications of an IAV infection including increased severity of the respiratory tract injury, and the risk of IAV-associated secondary bacterial pneumonia, a major cause of death in influenza cases. Specifically, we will examine the ability of 5?PPP-NS1shRNA nanoplexes to stimulate innate antiviral immunity, thereby changing infiltration of inflammatory cells, inflammatory cytokine milieu, adaptive immune responses, as well as decrease respiratory injury and IAV-associated impairment of bacterial clearance. In addition to assessing the clearance of IAV from the respiratory tract, we predict that the nanoplex construct will reduce the morbidity and severity of symptoms of influenza from drug resistant seasonal and pandemic strains, the highly pathogenic H1N1 swine-origin IAV virus (S-OIV) and H5N1 ?bird flu?. These nano-technological approaches can also potentially treat other infectious (i.e., Ebola) or non-infectious lung injuries. Our proposal is designed to produce a novel antiviral nanoplex formulation for Phase 1 clinical trials as an Investigational New Drug.